Riddle canon
A canon whose performing instructions (entries, intervals) are deliberately not notated and must be worked out by the performer.
What it means
A riddle canon (Latin canon aenigmaticus) is a canon in which the instructions for performance are deliberately not written out. Usually only one voice is notated, with a riddling inscription, a sign or an incomplete indication. The performer must find out for himself at what distance, at what interval or in which direction the other voices enter.
Musical use
Riddle canons were in the Renaissance and baroque a proof of contrapuntal skill and also a game for connoisseurs. Johann Sebastian Bach includes such canons in his Musical Offering (1747), for instance with the inscription Quaerendo invenietis ("Seek and you will find"). The solution might call for inversion, retrograde or lengthening of the note values.
The riddle canon should be distinguished from the simple canon, whose voice entries are written out or clearly marked, and from the fugue, which is worked freely in imitation.
Performance practice
If you want to solve a riddle canon, first examine the inscription and the signs. Try entry distances and intervals until all voices sound together. Check the solution for clean voice-leading, for only the right one gives a coherent texture.